Remote tuning of oscillator via duplex conductor



Feb. 2, 1960 c. G. soNTHx-:IMER 2,923,815

REMOTE TUNING OE OSOILLATOR VIE DUPLEX CONDUCTOR Filed Dec. l2. 1956 REMOTE TUNING OF OSCILLATOR VIA DUPLEX CONDUCTOR Carl G. Sontheimer, South Norwalk, Conn., assigner to C.G.S. Laboratories, Inc., Stamford, Conn.

Application December 12, 1956, Serial No. 627,947

6 Claims. (Cl. Z50- 20) This invention relates to electrical control systems and apparatus and is described as embodied in systems and apparatus for controlling one or more electrical circuits in unison. l

Controllable inductors have been used to control tuned circuits and have the advantage that by electrically Icontrolling the magnetic saturation of the core of the inductor, the effective value of the inductive portion ofthe tuned circuit can be controlled. Controllable inductors operate on the principle of a saturable reactor, 'but in the embodiments of the present invention described herein, they operate at substantially higher frequencies, as for example, in the radio frequency range. Such controllable inductors may use a core of ferromagnetic ceramic material, such as ferrite. This ferrite material may form all of the magnetic'circuit, or part of the magnetic circuit may be formed by other materials, such as iron. Suitable controllable inductors are .described in the following copending United States patent applications:

Serial No. 310,341 filed September 18, 1952, now Patent No. 2.886.789, 'dated May 12, 1959;

Serial No. 300,746 filed July 24, 1952, now APatent No. 2,802,185, dated August 6, 1957;

Serial No. 425,244 filed April 23, 1954, now Patent No. 2,869,087, dated lanuary 13, 1959; and

Serial No. 449,881 tiled August 16,1954.

Because such controllable inductors are sensitive to changes in ambient conditions,such as temperature, and are also affected by the hysteresis of the core material, it is desirable to provide a stabilized control current where precision operation of the inductor lis desired. For example, when a controllable'inductor system is used to tune a radio receiver and is provided with several separate signal windings controlled either by a single con- "trol winding or by Iseparate control windings, the individual circuits must track with eachother; that is, change inductance or tuning characteristics in unison. The current which is applied to the control winding desirably is regulated in such .manner that the adverse effect of` hysteresis, temperature changes, etc. are eliminated.

The present invention `provides a simple, effective system and apparatus for controlling such circuits so that a number of separate tuned circuits can be tuned readily to any desired frequency with maximum stabilizing characteristics, and rso that a number of separate tuned circuits -Sigual windings; and` f `United tts Patent i 2,923,815 lPatented Feb. 2 1960 Figure 2 shows a radio receiver incorporating the control circuit.

Figure 1 lshows an arrangement suitable for controlling the tuning of a superheterodyne radio receiver, for example, of the type described in my copending United States application, Serial No. 449,193, filed August 11, 1954, of which this application is a continuation-'in-part.

An alternating current signal is provided by a signal source 2, and the effective inductances of two signal windings 4 and 6 are made to vary in accordance with the frequency of the signal from the source 2. This source, for example, may be a vacuum tube or transistor oscillator in which the frequency is determined 'by the -inductance of a signal winding 3 of a controllable 'nductor 5. This oscillator circuit, for example, may -be similar to that described in my 'copending United yStates patent application, entitled Automobile Radio Receiver System Serial No. 445,146 filed July 22, 1954. The

output signal from the oscillator 2 at the terminal 7 'is applied through a blocking condenser 8 and through a shielded cable 10 having an electrically conductive shield 11 to a discriminator network, generally indicated at 12. If desired, this discriminator network 12 may be positioned remotely from the remainder of the receiver, as indicated. Preferably the terminal 7 is at a low impedance relative to ground for radio frequencies, and at substantially zero impedance for low alternating frequencies. For example, the terminal 7 can be a tap on a radio 'frequency coil, which is grounded at one end. Thus, the condenser 8 can advantageously serve as a hum bypass to remove hum voltages from the line 10.

The discriminator system 12 is arranged to produce a direct current control signal whose amplitude is a function of the frequency of the signal from the oscillator 2 relative to the frequency adjustment of the discriminator system. This D.-C. control signal also appears on'the cable 10 and is fed through an isolation resistor 13 and a lead 15 to a conventional vacuum tube or transistor D.-C. amplifier, indicated in block form at 16. The output terminals 18 and 20 of the amplifier 16 are connected to the control winding 22 of the controllable inductor 5 and to the control windings 24 and 26, respectively, of additional similar controllable inductors 28 and 30. Thus, as the control current delivered by the amplifier 16 varies, the magnetic saturation of the controllable inductors 5, 28 and 3f) is varied simultaneously. By this means,'the effective inductauce of the signal winding 3 and the effective inductance of the signal windings 4 and 6 of the inductors 28 and 30 are varied in unison, thus changing in unison the frequency of resonance of the tuned circuits formed by means of capacitors 36,38 and 40, each of which is connected in parallel with one of the signal windings 3, 4 and 6, respectively.

In brief, the D.-C. current through the control winding effects a partial saturation of the ferromagnetic material in the portions of the cores associated with the signal windings 3, 4, and 6. lf the magnitude of the con- `trol current is changed, the saturation of the portions of the core lmaterial-is changed accordingly and the signal winding coupled to the same core assumes a new :inductance value. In practice, the control current delivered by the amplifier 16 tojthe control windings 22, 24, and 26, when no error, i.e. control signal is applied through the input lead 15 to the amplifier V16 fis such as to bias the magnetic saturation of the .signal winding core p0rtions at about the mid-,point of the operating ranges of the respective signal windings.

This invention yis applicable to many different fields whereln tuned circuits are controlled in unison. For example, 1t has ,many ladvantages in tuning devices where yseveral resonant circuits are to be controlled iii-,accordfance with the frequency of an applied signal. In atypical frequency-selective circuit.

snperheterodyne radio receiver arrangement, the tuned circuit, of which the signal winding 3 forms a part, may be utilized to control the frequency of the signal generated by the local oscillator, represented in this example by the signal source 2. The tuned circuit of which the signal winding 4 forms a part may be utilized in the radio frequency amplifier stage ofthe receiver; and the other tuned circuit, of which the signal winding 6 forms a part, may be utilized in the antenna circuit of the radio receiver. In other words, the signal winding 6 is connected into the resonant circuit in lthe antenna stage of the receiver, and the signal winding 4 forms the inductive portion of a resonant circuit in a radio frequency amplifier stage of the receiver. In this particular example, it will be apparent that the antenna and radio frequency stages of the receiver will not be tuned to the same frequency as the local oscillator, but will diier therefrom by an amount equal to the intermediate frequency ofthe re-k ceiver. However, the antenna and radio frequency circuits must vary in unison with, that is they must track, the oscillator signal. This constant frequency difference can be maintained by the use of suitable padding and trimming inductances in connection with the signal winding 3, or in connection with the signal windings 4 and 6, as show in my above-identified copending application on the Automobile Radio Receiver System, and as explained in greater detail and claimed in the copending application Serial No. 454,256, filed September 7, 1954, in the name f.

of Raphael Gollub.

In operation, the tuning of the receiver to select the desired broadcast station is accomplished by varying the frequency response characteristics of the discriminator system, the details of which will be described more fully below.

In the discriminator system shown at l2 in' Figure l, a capacitor 42 is connected at a junction 43 in series with an inductor 44 between the cable 10 and the common return or so-called ground circuit. capacitor 42 and inductor 44 constitute a series resonant In this example, the tuning is accomplished by matinal adjustment of the inductor 44, for example, by moving a slug of magnetically permeable material in or out of the winding 44 in the manner conventional in the radio receiver art, such as by a screw feed actuated by a control knob or by substituting different inductors by means of push buttons. A halfwave rectifier 46, which may be a vacuum tube diode, has its anode 5G coupled through a capacitor 45 to the junction 43. Its cathode 48 is connected through a load resistor 52 to the anode 50. The capacitor 45 acts as a blocking and storage element and has capacitance which is large relative to the capacitance of the capacitor 42.

The signal voltage from the source 2 which appears across the inductor 44 thus is rectied and develops a charge on the capacitor 45 which, in turn, continuously discharges through the resistor 52. A resulting D.C. voltage appears across the resistor 52 with the polarity as indicated in the drawing.

Another similar rectifier 56 has its anode 58 connected to the junction of the capacitor 45 and the anode 50, and its cathode 60 is connected to the other terminal of the capacitor 42. A load resistor 62 is connected in parallel with the diode 56.

Thus, the signal voltage from the source 2 which appears across the capacitor 42 is rectified 'by the shunt diode 56, and a D.C. voltage appears across the load resistor 62 with the polarity as indicated.

It will be noted that the direct current voltages appearing across the resistors 62 and 52 are in opposition. Thus, the net output or error control voltage with respect to the common return, or ground circuit which appears at the cable terminal point indicated at 64 is the difference between these two opposed D.C. voltages.

When the resonant frequency of the series circuit` formed by the capacitor 42 and the inductor 44 is the Together, the .n

4 same as the frequency of the signal from the oscillator 2, then the voltage appearing across the capacitor 42 is equal to that developed across the inductor 44. Under these circumstances, the D.C. output control voltage at the cable terminal point 64 is zero.

When the resonant frequency of the series resonant frequency-selective circuit formed by the capacitor 42 and inductor 44 is higher than the frequency of the signal from the source 2, a negative control voltage appears at the point 64. When the resonant frequency of this series resonant circuit is lower than the frequency of the signal from the local oscillator 2, a positive control voltage is developed at the point 64.

There is thus generated an error signal which can be used for example to control the frequency of the signal generated by the source 2 in such manner that the frequency generated by this source is always equal to the resonant frequency of the series circuit formed by the inductor 44 and the capacitor 42. This same error signal will simultaneously control the inductors 28 and 30. The control voltage in this example is fed back to the D.C. amplifier 16 through the same connecting cable 10 and through the resistor 13, which has a resistance value which is high in comparison with the impedance of the line 10. A by-pass filter capacitor 66 is connected between the input terminal 67 of the control amplifier 16 and the common ground circuit. Thus, advantageously a single pair of wires, a coaxial line, or a shielded cable, whichever may be used in a particular installation, is enabled to carry both the A.C. signal from the source 2 to the discriminator system 12 and also to return the direct current control signal from the discriminator system 12 back to the control ampliier 16, although a separate return lead for the D.C. control signal can be used if desired.

The particular arrangement described is advantageous in remote operation because variations of the stray or shunt capacity appearing between the connecting cable 10 and the common ground circuit. have negligible effect on the operating frequency of the system. This highly desirable result is obtained because the inductor 44 and capacitor 42 are always tuned by the system so as to be resonant with the frequency of the signal from the source 2. The impedance across a series resonant circuit is 10W. Thus, the impedance at the point 64 is always low and effectively short circuits any undesirable effects which might otherwise be caused by such stray capacitances. v

Advantageonsly, the tunable discriminator circuit 12 always operates at the most sensitive portion of its range so that relatively large control signals are produced by very small deviations between the frequency of the signal source 2 and the resonant frequency of the discriminator network. The sensitivity of the tuning circuit shown increases as the ratio of the discriminator network is made larger in comparison with the source resistance of the source 2 as seen at the cable terminal 64 by the discriminator network 12. In practical tuning circuits the discriminator network 12 is made to have a relatively high Q which causes the voltages appearing across the inductor 44 and across the capacitor 42 to be'large when the applied frequencies are near the resonant frequency of the network. Thus a relatively large control voltage is produced at point 64 by relatively small changes in the frequency of the oscillator 2 with respect to the resonant frequency of the discriminator network 12.

Discriminator networks such as those shown in my above copending application, Serial No. 449,193 tiled August 1l, 1954, of which the present application forms a continuation-in-part, are suitable for use with the present invention. In that example, a signal winding of pacitor of different values.

'faenas te a controllable inductor forms `part of thediscriminator circuit, but from the foregoing disclosure, it will be `clear that this signal winding can be replaced by a rmanually adjustable inductor.

If desired, the inductor `44 is fixed in valuek and the capacitor 42 is used as an adjustable capacitor and the value of the capacitor 42 is varied to control the tuning of the system.

It will also be apparent that the positions of inductor 44 and capacitor 42 can be interchanged in the circuit shown, and that other circuit changes can be made in accordance with the teachings set forth above. `Various rectifier arrangements `well-known in the electronic art can be substitutedfor the arrangement shown in Figure 1.

It is apparent also that any desired means may be employed for changing the resonant frequency of the discriminator network and that other types of discriminator networks can be used, and that where desirable, more than one element of the discriminator network may be variable. For example, in the arrangement shown in Figure 1, it may in some instances'be desired to vary the values of both the capacitor 42 and the inductor 44, either simultaneously or individually.

It will be understood also that other devices may be utilized for controlling the frequency of the signal generated by the source 2 and that other types of controllable inductors can be substituted for the type illustrated. For example, an'inductor can be used such as that shown in my above-identified application, SerialI No.

449,193 in which three separate signal windings are operatively associated with a single control winding.

Figure 2 shows the application of this tuning arrange'- 'rnent to a radio receiver.V An antenna 72 is connected `to the antenna stage 74 of a superheterodyne receiver `stage 76, and the antenna stage 74 are tuned 'b3/.means of a controllable inductor 5A.

The frequency-sensitive discriminator network 12 is the same as that described in connection with Figure 1, except that in this example the capacitor 42 is indicated as being variable and the inductor 44 is shown as .firedin value.

In this example, the controllable inductor 5A includes a control winding 22A and has three separate signal windings 3A, 4A and 6A, which are controlled in unison by the current in the winding 22A.

In operation, the radio transmitting station to be received is selected by varying the capacitor 42, either by means of a continuously manually variable capacitor, or by means of push buttons arranged to substitute ca- For any setting of capacitor 42, the D.C. amplifier 1l6 is actuated by the error i.e. control signal from the discriminator network 12 and sends a direct current through the control winding 22A to adjust the inductance of the signal winding 3A to that value which will cause the local oscillator to operate substantially at the resonant frequency of the series resonant network formed by the capacitor 42 and inductor 44. This same control winding 22A also simultaneously adjusts the inductances of the signal windings 4A and 6A to the correct values to tune the antenna and radio frequency amplifier stages to the proper 'of which is manually adjustable in value, and rectification means coupled to said series resonant circuit and Yarranged to produce a D.C. control signal whose amplitude is a function of the frequency of the signal generated by said source, said rectification means supplying said D.-C. control signal to said conductor, and means connecting said conductor to said frequency-determining means.

2. A control system comprising electrically controllable inductor means having control winding means and 'a plurality of separate signal windings, a source of alternating current signals having frequency-determining means `including one of said signal windings, an electrical conductor coupled to said source and extending to a position remote from said sour-ce, a discriminator system located at said remote position and being coupled to said source of signals through said electrical conductor, said discriminator including a series-resonant circuit having inductance and capacitance means `at least `one of which is manually adjustable in value, and rectification means coupled to said series-resonant circuit and arranged to produce a D.C. -control signal whose amplitude is a function of the frequency of the signal generated by said source, said rectification means being connectedito said conductor and supplying said D.C. control Signal to said conductor, and circuit means connecting said conductor to said control winding means.

3. In a radio receiver having an antenna stage, a radio frequency stage, and a local oscillator, apparatus comprising electrically controllable inductor means having control winding means and first, second and third signal windings respectively forming parts of said antenna stage, radio frequency stage, and local oscillator; an electrical conductor coupled to said local oscillator and extending to a position remote from said local oscillator; a discriminator system located remotely from said local oscillator and being coupled throughsaid electrical conductor to .saidlocal oscilaltor, said discriminator including a series-resonant circuit having inductance and capacitance means at least one of which ismanually adjustable in value, and rectification means coupled to said series-resonant circuit and arranged to produce a D.-C. control signal whose amplitude is a function of the frequency of the signal generated by said source, the output of said rectification means being connected to said electrical conductor at Said remote position, and means coupling said electrical conductor to said control winding means.

4. In a radio receiver a tuning system comprising a controllable inductor having a control winding, first, second and third signal windings, an antenna stage having a tuned circuit including said first signal winding, an R-F stage having a tuned circuit including said second signal winding, a local oscillator having a tuned circuit including said third signal winding, an electrical conductor connected to said local oscillator,-said conductor having a portion remote from said oscillator, a discriminator system coupled to said remote portion of the conductor, said discriminator including a series-resonant circuit comprising at least one capacitorand at least one inductor, at least one of which is manually adjustable in value, a first rectifier connected to said capacitor and arranged to produce a first direct voltage, the amplitude of which is a function of the amplitude of a signal from said oscillator appearing across said capacitor, a second rw bining said first and second direct voltages in opposition to produce a resultant control signal whose amplitude is a function of the difference between the frequency of the signal produced by said local oscillator and the resonant frequency of said series-resonant circuit, said means being connected to said remote portion of the conductor, a direct current amplifier connected to said conductor and under the control of said resultant control signal, and means connecting said control winding to the output of said direct current amplifier.

5. An improved tuning system for a radio receiver having an antenna, a radio frequency circuit coupled to the antenna and a local oscillator and mixer circuit coupled to the radio frequency circuit, said improved tuning system including a controllable inductor having first and second signal windings associated with magnetically saturable core portions and control Winding means magnetically coupled to said core portions and regulating the degree of saturation of said core portions and controlling the effective inductance of said signal windings in accordance with a control current therein, said first signal winding being included in said oscillator and mixer circuit and controlling the frequency generated therein, and said second signal winding being included in said radio frequency circuit and controlling the tuning thereof, an electrical conductor connected to said oscillator and mixer circuit, circuit means connecting said electrical conductor to said control winding means, said conductor extending to a position remote from said oscillator and mixer circuit, a frequency-responsive network positioned remotely from said oscillator and mixer circuit, said network including an inductance element in Series witha capacitance element coupled to said electrical conductor and sensing the frequency generated in said oscillator and mixer circuit, first rectifier means coupled to said inductance element and producing a first direct voltage, the amplitude of which is a function of said generated frequency, second rectifier means coupled to said capacitance element and producing a second direct voltage, the amplitude of which is a function of said generated frequency, and means connected to said electrical conductor for combining said first and second direct voltages in opposition to produce a control signal Whose value is a measure of the difference between the frequency generated in said oscillator and mixer circuit and the resonant frequency of said frequency-responsive network, said control signal being conducted by said electrical conductor for regulating the value ofthe control current in said control winding means, one of said elements in said frequency responsive network being adjustable as desired by the operator, thereby tuning said radio receiver.

6. An improved tuning system for a radio receiver having an antenna, a radio frequency circuit coupled kto the antenna and a local oscillator circuit coupled to the radio frequency circuit, said improved tuning system including a controllable inductor having first and second signal windings associated with magnetically saturable core portions and control winding means magnetically coupled to said core portions and regulating the degree of saturation of said core portions and controlling the effective inductance of said signal windings in accordance with a control current therein, said first signal winding being included in said oscillator and mixer circuit and controlling the frequency generated therein, and said second signal winding being included in said radio frequency circuit and controlling the tuning thereof, an electrical 4 conductor extending from said oscillator circuit to a remote position, a frequency-responsive network positioned remotely from said oscillator and including an inductance element in series with a capacitance element coupled to said conductor and sensing the frequency generated in said oscillator circuit, rectifier means coupled to said inductance and capacitor elements and producing a direct voltage whose value is a measure of the difference between the oscillator frequency and the resonant frequency of said frequency-responsive network, current amplification means having its output connected to said lcontrol winding means, said direct voltage being fed back through said conductor to the input of said current amplification means for regulating the value of the control current in said control Winding means, one of said elements insaid network being' adjustable as desired for tuning the receiver.

References Cited in the le of this patent UNITED STATES PATENTS 1,780,669 Bruckel Nov. 4, 1930 2,056,011 Lowell Sept 29, 1936 2,152,336 Van Loon Mar. 28, 1939 2,190,319 Koch Feb. 13, 1940 2,287,925 White June 30, 1942 2,302,893 Van Roberts Nov. 24,1942 2,320,996 Alexanderson .lune 8, 1943 2,601,384 Goodrich Jan. 24, 1952 2,839,684 Smith-Vaniz v June 17, 1,958 

